Insulation, energy storage and ventilation that work for my clients.

In short: Good a Basement Air tightness MHRV mechanical heat recovery ventilation Internal insulation Solar panels Storing the cheapest energy from the grid Wise use of concrete   Bad Thermal Mass Air source heat pumps Ground source heat pumps Storing heat in the ground I have another page about these things that do not work here.

1. air tight
2. 400mm of insulation and triple glazed windows
3. winter sun maximised
4. summer sun reduced
5. mechanical heat recovery ventilation (note that the unit should be easily accessible so that the filter can be vacuumed to remove lint fortnightly and filters changed easily 4 times a year)
6. no cold bridges or energy leaks

Over 30 years ago, the Building Research Establishment, BRE, produced a paper about the U value of a basement without insulation. The U Value of an average domestic basement, just because it is buried, is about 0.16 before you add any insulation. The point, therefore, is that a basement neither needs much insulation nor much heating. Quote this leaflet and insist that a sensible figure is used for your basement before you choose insulation. Don't let someone charging you good money for their 'expertise' fob you off saying it wasn't included in their training, therefore insulation by the ground doesn't exist. Because it does. Click on each image to open full size images in new tabs.

This is an example of a thermal bridge except that the insulation against the basement wall impedes heat loss into the concrete. Note also from the Thermal Mass section, 8, on the other page. If the concrete is totally dense, because it is known to be Waterproof, then heat would escape very slowly compared to escaping through other building materials. The thermal bridge in my image is not particularly bad if the concrete is waterproof, that is, maximum possible density. The U Value of 150mm of properly waterproof concrete is probably about 0.25. Not sufficient on its own, but enough to reduce the insulation that needs to cover it.

4. Good insulation strategy.

(From a German website) "Important factors in the refurbishment of the building envelope are the insulating material, the avoidance of thermal bridging, windows and glass constructions and a high degree of air-tightness overall. Key considerations in all cases are an individual evaluation of the entire building and skilled, professional planning and realisation."

For Realisation, I read supervision and workmanship.

Years ago, a client mentioned that a good friend of his is a Professor of Environmental Engineering. Shortly after, I received this paragraph, presumably aimed at the client but with my web page in mind. "Putting the concrete on the room side of the insulation (ie ground-insulation-concrete-room) it will retain heat (like a storage heater) and reduce the rate (speed) at which the overall room cools down and heats up. It will make no difference (over a season) how much heat you use to heat the basement (if its kept at a reasonably constant temperature). It will take longer to heat if you allow the basement to cool down so if you wanted to use the basement infrequently for short periods (eg as a spare bedroom) and then leave it empty (and cool) then it may not be the best solution (although that could be overcome by adding more insulation internally)." I think that if the entire dwelling is a box of waterproof, that is extremely dense, concrete. It will be totally air tight. If it is insulated sufficiently all over the inside you are only ever heating the air.

Basement Floor Insulation.

For building regs approval you will need to show floor insulation over the structural floor slab.

But I promise you that many of my clients haven't got round to it yet because their basement is warm enough and they prefer the extra headroom.

There are 3 choices.

1. Insulation over the structural floor slab beneath the screed. The usual.


2. Insulation under the structural floor slab. A screed is still necessary to get a flat floor because it is not possible to get a perfectly flat floor with waterproof structural concrete that is stiff and sets quickly. (Although doubling the dose of my powder in waterproof concrete for £69 per cubic metre certainly helps).


3. No insulation. Relying on at least 2m of soil between the floor and the open air.

It is proven in the BRE leaflet that 2m of soil between the basement structure and the open air is sufficient insulation.



Concreting tip. If you are pouring floor concrete over insulation boards, and concrete that gets between the boards will make them float up lifting the reinforcing steel with it.

Put polythene over the insulation before the steel. You will tear it in a few places, but mainly the concrete won't get down between the boards.

Cavity Wall Insulation. Another gem of a simple idea from my happy MHRV customer. He put his cavity wall insulation in himself. His inner masonry leaf is blockwork. the cavity insulation is 50mm of rockwool then 150mm of insulation board, such as Celotex, QuinnTherm or Recticel, then his cavity then his brick. He explained that the rockwool follows the contours of his blockwork, ensures no air gap between the blockwork and his rigid board and ensures that joints in his rigid board are closed by rockwool.

1. Get yourself a free solar panel set fitted and paid for by your electricity supplier.


2. Then get it disconnected from the mains and adapted to charge up an array of batteries you buy yourself.


3. Sell electricity to EV owners by listing yourself on Zapmap. Or use it instead of petrol yourself.

1. Store energy in batteries. If you already have an EV, you already have batteries.


2. Store energy to heat your water. I am going to suggest in a ZEB.

This is the Zero Emissions Boiler, ZEB, from Tepeo. This ZEB costs about £5,000 and you more or less just connect it to your existing plumbing. It doesn't need a heat pump. Cold water flows in and hot water flows out. Tepeo claim that they use electricity (off-peak, at its cheapest) to heat their store to 800°C. An air source heat pump will currently cost you about £13,500 plus new radiators and so on, less the grant of £7,500, meaning it costs more than £6,000. However, there is a new generation of air source heat pumps that extract heat successfully even when it is below freezing outside and you don't need to buy new, bigger radiators. I don't have any costings. Currently, government policy is that you get a good SAP score for a heat pump that will destroy our infrastructure, and a bad SAP score for a ZEB that will save it. On my page about what fails, I explain why heat pumps fail. Basically, when we have freezing temperatures, heat pumps use more electricity from the grid than the heat they bring in. Dreadfully inefficient. But when more of us have a heat pump and it is very cold outside they will demand so much electricity the grid will fail and we will have blackouts and freeze. Storage heaters have a reputation for not delivering heat as you need it they are still available and there is a special tariff from British Gas if you have Dimplex heaters here.

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